The deposition of organic contaminants (i.e., pitch and stickies) on surfaces in the papermaking process is well known to be detrimental to both product quality and the efficiency of the papermaking process. Some contaminating components occur naturally in wood and are released during various pulping and papermaking processes. Two specific manifestations of this problem are referred to as pitch (primarily natural resins) and stickies (adhesives or coatings from recycled paper). Pitch and stickies have the potential to cause problems with deposition, quality, and efficiency in the process as mentioned above.
The term “pitch” can be used to refer to deposits composed of organic constituents which may originate from these natural resins, their salts, as well as coating binders, sizing agents, and defoaming chemicals which may be found in the pulp. In addition, pitch frequently contains inorganic components such as calcium carbonate, talc, clays, titanium and related materials.
Stickies is a term that has been increasingly used to describe deposits that occur in the systems using recycled fiber. These deposits often contain the same materials found in “pitch” deposits as well as adhesives, hot melts, waxes, and inks.
The deposition of organic contaminants, such as pitch and stickies, can be detrimental to the efficiency of a pulp or paper mill causing both reduced quality and reduced operating efficiency. Organic contaminants can deposit on process equipment in papermaking systems resulting in operational difficulties in the systems. The deposition of organic contaminants on consistency regulators and other instrument probes can render these components useless. Deposits on screens can reduce throughput and upset operation of the system. This deposition can occur not only on metal surfaces in the system, but also on plastic and synthetic surfaces such as machine wires, felts, foils, Uhle boxes and head box components.
Historically, the subsets of the organic deposit problems, “pitch” and “stickies”, have manifested themselves separately, differently and have been treated distinctly and separately. From a physical standpoint, “pitch” deposits have usually formed from microscopic particles of adhesive material (natural or man-made) in the stock which accumulate on papermaking or pulping equipment. These deposits can readily be found on stock chest walls, paper machine foils, Uhle boxes, paper machine wires, wet press felts, dryer felts, dryer cans, and calendar stacks. The difficulties related to these deposits included direct interference with the efficiency of the contaminated surface, therefore, reduced production, as well as holes, dirt, and other sheet defects that reduce the quality and usefulness of the paper for operations that follow like coating, converting or printing.
From a physical standpoint, “stickies” have usually been particles of visible or nearly visible size in the stock which originate from the recycled fiber. These deposits tend to accumulate on many of the same surfaces that “pitch” can be found on and causes many of the same difficulties that “pitch” can cause. The most severe “stickies” related deposits however tend to be found on paper machine wires, wet felts, dryer felts and dryer cans.
Methods of preventing the build-up of deposits on the pulp and paper mill equipment and surfaces are of great importance to the industry. The paper machines could be shut down for cleaning, but ceasing operation for cleaning is undesirable because of the consequential loss of productivity, poor quality while partially contaminated and “dirt” which occurs when deposits break off and become incorporated in the sheet. Preventing deposition is thus greatly preferred where it can be effectively practiced.
Poly[vinyl alcohol-co-vinyl acetate] is shown to be effective in controlling the deposition of pitch and stickies contaminants from pulp and papermaking systems in U.S. Pat. Nos. 4,871,424 and 4,886,575, respectively.
U.S. Pat. Nos. 4,184,912 and 4,861,429 teach methods of inhibiting organic contaminant deposition in pulp and papermaking systems by the addition of multi-component compositions comprising in part a non-ionic surfactant.
European Patent Application 0 568 229 A1 claims a method for inhibiting the deposition of organic contaminants from pulp and paper making system comprising treatment with a hydrophobically modified polymer including polyethylene oxide polymers functionalized with hydrophobic groups connected via an ester linkage.
Chemical Abstract Number 82:18,896 refers to a method for removing pitch from pulp comprising treatment with polyethylene glycol alkyl ether surfactant derived by reacting a secondary alcohol with alkyl glycidyl ether.
U.S. Pat. No. 6,482,994 B2 teaches that ethoxylated alcohols surfactants which are ether-capped by reaction with glycidyl ether provide superior grease cleaning abilities and improved spotting/filming benefits in dishwashing applications.
U.S. Pat. Application 2005/0150418 A1 claims a polymer composition comprising water-soluble or water-swellable synthetic polymer backbone that has covalently connected ends and/or intermediate blocks of oligomeric hydrophobes wherein the blocks are composed of two or more units of hydrophobes. These hydrophobically associative polymers are taught to enhance the thickening, leveling, and sag properties of waterborne coatings. The examples of the polymer composition included the reaction products of polyethylene glycols and aryl glycidyl ethers and alkyl epoxides. The 5 weight % aqueous solution viscosities of these materials in the examples ranged from 19,000 cps to >400,000 cps. Included in the list of typical applications where these polymer compositions may find utility included pitch control in pulping.
A drawback to the prior art is that the poly[vinyl alcohol-co-vinyl acetate] is susceptible to further hydrolysis under pulp and papermaking environments which reduces its efficacy. The polyethylene glycol based non-ionic surfactants cited are also typically utilized in multi-component formulations and also contain functionalities susceptible to hydrolysis. In addition, the solution viscosities of the hydrophobically modified polyethylene glycol associative polymers are too high to make their use practical from a commercial perspective.